Fuse plug



R. BROWN Och 1933.

USE PLUG Filed Aug 9,

. Z% w W a Invento George RB AttOYneH Patented Oct. 3, 1933 UNITED STATES FUSE PLUG George R. Brown, Bridgeport, Conn, assignor to General Electric Company, a corporation of New York Application August 9, 1929. Serial No. 384,720

3 Claims. (01. 200-130) The present invention relates to electrical safety devices and more especially to fuse plugs.

The object of my invention is the provision of an improved fuse plug which shall effectually prevent escape of gases of fusion upon blowing under severest circuit conditions, and which shall permit at all times of ready inspection of the fusible element.

One embodiment of the invention is shown in the accompanying drawing in which Fig. 1 is a side elevation of the plug; Fig. 2'is a vertical section; Fig. 3 is a plan view of the plug with the upper. portion removed, and Fig. 4 is a top plan view of the complete plug.

As shown in the drawing, the insulating enclosure of the plug is composed of a base 1 and a chambered upper part 2, and on which center v and screw shell contacts 3 and 4 are mounted and connected by a fusible element 5.

The base 1 is made preferably of pure white porcelain and comprises a central disk 6 with a relatively high cylindrical flange '7 extending upwardly thereof and a polygonal knob 8 on the lower side thereof.

The center contact 3 is in the form of a metal eyelet or shell upset in an axial bore of the disk 6 and knob 8. t

The fusible element 5 consists of a strip of flat metal having a central contracted section 9 and 30 one end secured within the center contact 3 by a slug 10 of lead or solder. The metal strips customarily have impressed thereon indicia 11 of their rated capacity and such indicia are preferably located near the contracted section 9 so that both will be located in the horizontal part of the strips as they extend out across the upper end of cylindrical flange 7.

The chambered upper part 2 is made in the shape of an inverted cup with a flat top having a peripheral hand hold 12 and helical threads 13 about its lower end. A vertical groove 14 is formed in the outer surface which traverses the threads 13, so that the outer end of the fusible element 5 may be seated therein while the flanged screw shell contact 4 is screwed upon the helical threads 13 to thereby firmly clamp the base disk 6 against the lower end of the chambered part 2. A slug of solder 15 applied in the upper end of the groove-14 serves electrically to connect the fusible 50 to prevent unscrewing of the contact 4 from the chambered part 2.

In order that ready inspection of the condition of the fusible element 5 may be had, the chambered part 2 is made of transparent material and provided in the upper end with an integral plano convex lens 16 which serves to magnify the size of the fusible element and especially of any gap that may be formed therein upon blowing. The transparent material is high silicon glass, comelement 5 to the screw shell 4 and mechanically mercially known as Pyrex, which is highly resistive of fracture and which has a very low coeflicient of expansion whereby it is adapted to withstand the sudden and localized changes in temperature incident to blowing of the fuse without cracking. Moreover, it is non-hydroscopic and in consequence of which it does not become coated with dust and soot or otherwise lose its clear transparency. By making the base 1 of pure white porcelain, the interior of the plug shows white through the lens 16 until disruption of the fusible element occurs which ordinarily produces a blackening of the interior surfaces. However, in case the amount of metal volatilized upon blowing is insufficient to produce noticeable blackening, the small break in the fusible element is sufficiently magnified by the lens to render it readily observable, substantially as indicated in Fig. 4 of the drawing.

On account of the great strength and hardiness of my plug, it is unnecessary to provide it with vents or other means commonly employed for cushioning or moderating the effect of the high gas pressures incident to blowing under short circuit conditions.

While I have shown and described the best embodiment of the invention known to me, I do not desire to be restricted thereto.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A fuse plug comprising an insulating base, a chambered upper part of transparent high silica glass of low expansion coefficient and having an integral lens in the wall thereof whose surfaces are of substantially differing curvature to produce substantial magnifying effect in the direction of the gap which is formed in the fusible element when it is blown to provide for ready inspection of the condition of the fusible element, center and screw shell contacts mounted on the fuse plug and a fusible element located within the plug opposite said lens and electrically connecting said contacts.

2. A fuse plug comprising a base of white insulation, a chambered upper part of transparent high silica glass of low expansion coefficient and having an integral spherical lens in the end wall thereof of substantial magnifying effect, center and screw shell contacts mounted on said insulating parts, and a fusible element located opposite said lens within the chamber formed by said insulating parts and electrically connecting said contacts.

3. A fuse plug having a chambered insulating part with an integral spherical lens of substantial magnifying effect composed of high silica glass.

GEORGE R. BROWN. 

